The apparatus and method disclosed herein, in general, relates to manufacturing composites.
In the current art of vacuum assisted resin transfer molding, a breather layer is used for removing excess resin and for providing a medium for removal of entrapped air in a composite. The breather layer is usually a sacrificial layer that increases the cost of manufacturing. There is a need to eliminate the use of such breather layers in the vacuum assisted resin transfer molding process. A semi-permeable membrane that is permeable to air, but impermeable to resins may replace the use of breather layers in the vacuum assisted resin transfer molding process. However, such semi-permeable membranes have a limited life, are expensive, and require proper handing. The placement and removal of a semi-permeable membrane below a vacuum bag used in the vacuum assisted resin transfer molding process is an additional manufacturing process that needs to be avoided. If a resin were to be injected in a channel in the vacuum assisted resin transfer molding process, the resin will travel a limited distance from the channel and the casting of large areas is not possible using a single channel. If multiple channels are used, there is a significant risk of air entrapment between resin fronts radiating from different channels. Hence, there is an unmet need for a vacuum assisted resin transfer molding process for the manufacture of large areas of composites, which minimizes the entrapment of air and the creation of pores and cavities within the composites, with a reduction in the use of breather layers and semi permeable membranes.
Resin composites are commonly manufactured using resin transfer molding by injecting a cast material, for example, a fiber composite, with resin under a vacuum. In most end applications, it is critical that the resin is evenly infused in the entire section of the cast material. If excess resin is injected in certain sections of the cast material, the excess resin may result in part rejects or an increase in costs. In resin transfer molding systems, there is an unmet need to efficiently reduce resin rich or resin excess areas.
Typically, in the vacuum assisted resin transfer molding process, resin is injected at a negative pressure, which avoids lifting a top sheet of the vacuum bag during resin injection with excess resin due to a hydraulic head created by an input resin reservoir. Injecting resin at positive pressure has its advantages, for example, in increasing a resin infusion rate. In such positive pressure resin injection systems, there is an unmet need to reduce resin rich or resin excess areas created by the undesirable lifting of the top release sheet of the mold.
The mold cycle time must be minimized in order to produce articles economically. Some of the activities that negatively affect the mold cycle time comprises using tacky tapes for sealing, utilizing “use and throw” resin channels, cleaning resin flash, and lifting, placement, positioning, and using tapes for sealing of the vacuum bag. There is an unmet need to reduce or obviate the need for the above steps.
The injected resin in a high temperature based vacuum assisted process may rapidly gel. It is necessary that the resin travels the entire section of the mold cavity and fully encompasses the cast material before the resin gels. Therefore, there is a need for a method and an apparatus that permit rapid flow of the resin throughout the mold.
In the current art, vacuum bags are used in vacuum assisted resin transfer molding processes. In U.S. Pat. No. 7,189,345, the term “inflatable bladder” has been synonymously used with the term “vacuum bag”. The “inflatable bladder” as defined in line 3, column 3 of U.S. Pat. No. 7,189,345 is “commonly referred to as vacuum bag”. In FIG. 1 and FIG. 2 of U.S. Pat. No. 7,189,345, this “inflatable bladder” is nothing but a regular vacuum bag, similar in construction to the inflatable bladder shown in FIG. 4. In FIG. 4 of U.S. Pat. No. 7,189,345, the outer edges of the inflatable bladder defined by the numeral 108 create a vacuum seal. In FIG. 4, it can be seen that the edges of the inflatable bladder seals with the tool surface. In FIG. 4, the inflatable bladder is illustrated as a sheet with defined and cut edges, indicating that the inflatable bladder is a sheet with edges. It implies that within itself, the inflatable bladder is not a closed system. However, when the inflatable bladder seals with the hard surface of the mold, a closed system develops between the sheet and the hard surface. In column 1, lines 55 to 56, U.S. Pat. No. 7,189,345 states that the “bladder has a resin inlet with fluid communication with the cavity”. In column 5, lines 8 to 10, U.S. Pat. No. 7,189,345 states that “vacuum applied to the mold cavity forces the bladder against the composite structure . . . ”. There is no reference whatsoever in the entirety of U.S. Pat. No. 7,189,345 to use positive pneumatic pressure or compressed air to press the bladder against the mold cavity. Furthermore, there is no reference whatsoever in the entirety of U.S. Pat. No. 7,189,345 to compressed air being enclosed in a closed system for the application of pressure.
Therefore, there is a long felt but unresolved need for an apparatus and method that enables manufacture of large areas of composites, which minimizes the entrapment of air and the creation of pores and cavities within the composites, efficiently reduces resin rich or resin excess areas in the composite, and permits rapid flow of resin throughout the composite.